1. Field of the Invention
The present invention relates to a printing apparatus and a transporting mechanism for transporting continuous paper, and more particularly to a printing apparatus having a continuous-paper transporting mechanism for stably transporting continuous paper which is not provided with feeding perforations, as well as a continuous-paper transporting mechanism suitable for use in such a printing apparatus.
2. Description of the Related Art
Conventionally, in cases where continuous paper is printed by a printer, feeding perforations provided continuously at equal intervals in the feeding direction are provided in advance on each side of the continuous paper. Meanwhile, a tractor having pins which fit in the feeding perforations in the continuous paper is provided on the printer side, and the continuous paper is transported as this tractor rotates.
For this reason, predetermined feeding perforations must be provided in the paper. In addition, not only are portions at both side edges of the paper unable to be used for printing, but they become unnecessary after printing, so that they must be disposed of by such as cutting the both side edge portions in post-processing. For this reason, there has been a demand for a technique for transporting continuous paper which is free of feeding perforations from the viewpoint of paper processing cost and the like.
a conventional technique for transporting continuous paper which is free of feeding perforations is disclosed in JP-T-9-507666. The technique disclosed in the document JP-T-9-507666 is shown in FIG. 2.
In FIG. 2, reference symbol “A” denotes paper; reference symbol “PZ” denotes a paper device; reference symbol “DA” denotes a printing unit; reference numbers 1 and 11 denotes a paper input device; reference numbers 2 and 4 denotes rollers; reference number 3 denotes a paper centering device; reference number 6 denotes a vacuum brake; reference number 7 denotes a vacuum pump; reference number 8 denotes a friction drive; reference number 9 denotes a stabilization roller; and reference number 10 denotes a festoon device.
The mechanism for transporting continuous paper free of feeding perforations is provided with a paper braking member (vacuum brake 6) for braking the paper with respect to the transporting direction by sucking the continuous paper between the friction drive, i.e., the pair of drive rollers 8, and the upstream side of the pair of drive rollers 8. In a course of the continuous paper, a paper-position restricting mechanism (centering device 3) is provided for keeping the position of the paper at a prescribed position in a direction perpendicular to the paper transporting direction. The paper-position restricting mechanism is constituted by the pair of rollers 4 disposed obliquely at an angle θ with respect to the paper feeding direction.
The vacuum brake 6, the mechanical accumulator 9, the festoon device 10 for imparting tension to the paper are respectively provided between the paper-position restricting mechanism 3 and the pair of frictionally transporting drive rollers 8, so as to fix the tension of the paper and stabilize the paper transport.
Here, in the continuous paper printing apparatus, at the time of the starting or stopping of printing, certain time is required for achieving build-up to a fixed speed or stopping from the fixed speed in the light of the characteristics of a transport motor for driving the paper transport. Therefore, control is provided in which build-up is achieved up to a fixed speed while the continuous paper is transported a certain length A, and the transport is stopped at a point of time when the continuous paper has been transported a certain length B at the time of stopping. To eliminate the positional offset A+B of the paper at the time of the starting or stopping of printing, control is generally provided such that the continuous paper is transported in the opposite direction by a portion corresponding to the length of A+B, to thereby effect printing continuously without providing wasteful margins.
In the known example described above, when a slack occurs in the continuous paper at the time when the paper is transported in the opposite direction, paper skew occurs, and the traveling of the paper ceases to be stable. Therefore, the paper-position restricting mechanism absorbs the paper slack by unit of the festoon device 10 to suppress the slack of the paper, thereby preventing the paper skew.
Other examples disclosed in JP-A-7-247045 and in JP-A-9-086742 are known as a conventional technique. The document JP-A-7-247045 discloses that the operation and releasing of a curl straightening mechanism for recording paper are effected by a simple mechanism, and that a pressure contact roller is reversely rotated to improve the filing characteristic of the recording paper. Namely, as a unit for releasing the recording paper from the curl straightening mechanism, the recording paper is fed in the opposite direction after completion of recording, and the recording paper is moved away from an inverse warping part of the curl straightening mechanism, thereby preventing a curl from being formed at the time of non-recording.
In the document JP-A-9-086742, in a continuous paper transporting mechanism having a paper feed tractor for transporting continuous paper from a hopper toward a photosensitive drum, to prevent the dislocation of the continuous paper and prevent the occurrence of transfer bleeding at the time of a printing start, a paper braking member is provided for braking the continuous paper in the transporting direction by pinching the paper surface of the continuous paper on the upstream side of the paper feed tractor, and a buffer unit for absorbing the slack of the continuous paper is spring-urged between this paper braking member and the paper feed tractor so as to constantly come into contact with the paper surface of the continuous paper and push it out.
However, the known example (FIG. 2) disclosed in the document JP-T-9-507666 has the following drawback.
Since the vacuum brake 6, the mechanical accumulator 9, and the festoon device 10 are respectively provided for imparting tension to the paper, the number of component parts increases, so that the cost and size of the apparatus become large.
End faces of the paper are positioned by the paper-position restricting mechanism 3, and the paper is transported by the pair of frictionally transporting drive rollers 8. However, since the accumulator 9 arranged so as to allow the paper to be wound therearound, a roller provided in the festoon device 10, and the like are present between the paper-position restricting mechanism 3 and the pair of frictionally transporting drive rollers 8, paper skew components are generated with respect to the direction of transport by these rollers, so that the parts accuracy and the mounting accuracy of the respective rollers must set strictly.
In addition, since the position of a swing roller provided in the festoon device 9 of the accumulator changes during printing, and the amount of paper wound around the roller changes. Therefore, the skew component imparted by the swing roller to the paper changes due to the amount of paper wound around the moving roller, so that the drifting action of this portion is unavoidable.
In addition, as a conventional known method other than the known examples described above, there is a technique in which, instead of providing the paper braking member on the upstream side of the pair of frictionally transporting drive rollers, a transporting mechanism is provided for effecting the transport of paper to a hopper section, and control is provided so as to reversely transport the paper at the time of back feeding of the paper. However, according to this method, at the time of reverse transport, the driving of the paper-position restricting mechanism consisting of a pair of rollers disposed obliquely with respect to the paper transporting direction is controlled, and the setting of an angle θ with respect to the paper transporting direction must be changed. Therefore, the mechanism and the controlling method become complex, the number of components increases, and the size of the apparatus also becomes disadvantageous.